Ground robot drive system

ABSTRACT

A ground robot having a main body, two opposing drive systems, a flipper disposed distal to the main body, and a front wheel and a rear wheel, both disposed substantially parallel to the vertical plane and between the inner track and the flipper. The main body has a sagittal plane and two opposing lateral sides. Each drive system having an inner track disposed proximal to the main body. The inner track extends along a corresponding lateral side of the two opposing lateral sides and substantially parallel to a vertical plane of the main body, and is supported by a plurality of inner pulleys. The flipper extending along the corresponding lateral side and substantially parallel to the vertical plane. The flipper has a flipper body, an outer track, and a plurality of outer pulleys supporting the outer track. The diameter of the front wheel and the rear wheel of each of the opposing drive systems ranges between 1.2 to 1.3 times of a diameter of the inner track.

FIELD OF THE INVENTION

The present invention relates to the field of tracked drive systems.

BACKGROUND

Ground robots face many challenges when attempting mobility. Terrain canvary widely, including for example, loose and shifting materials,obstacles, vegetation, limited width openings, limited height openings,steps, uneven surfaces, tunnels, holes and the like. A variety ofmobility configurations have been adapted to transverse difficultterrain. These options include legs, wheels and tracks. Legged robotscan be agile, but use complex control mechanisms to move and achievestability. Tracked robots have traditionally been configured in atank-like configuration. Flippers are also used in robotic platforms forclimbing obstacles such as stairs, rocks and slopes.

The foregoing examples of the related art and limitations relatedtherewith are intended to be illustrative and not exclusive. Otherlimitations of the related art will become apparent to those of skill inthe art upon a reading of the specification and a study of the figures.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools and methods which aremeant to be exemplary and illustrative, not limiting in scope.

There is provided, in accordance with an embodiment, a ground robotcomprising: a main body having a sagittal plane and two opposing lateralsides; two opposing drive systems, each located at one of said twoopposing lateral sides and each comprising: an inner track disposedproximal to the main body, the inner track extending along acorresponding lateral side of the two opposing lateral sides andsubstantially parallel to a vertical plane of the main body, wherein theinner track is supported by a plurality of inner pulleys; a flipperdisposed distal to the main body, the flipper extending along thecorresponding lateral side and substantially parallel to the verticalplane, wherein the flipper comprises: a flipper body, an outer track,and a plurality of outer pulleys supporting the outer track; and a frontwheel and a rear wheel, both disposed substantially parallel to thevertical plane and between the inner track and the flipper, wherein adiameter of the front wheel and the rear wheel of each of the opposingdrive systems ranges between 1.2 to 1.3 times of a diameter of the innertrack.

In some embodiments, each of the front wheel and the rear wheelcomprises, on an external surface thereof, a plurality of wheelprojections.

In some embodiments, the inner track comprises, on an external surfacethereof, a plurality of inner track projections protruding outwards withrespect to the inner track.

In some embodiments, the outer track comprises, on an external surfacethereof, a plurality of outer track projections protruding outwards withrespect to the outer track.

In some embodiments, the diameter of the inner track of each of the twoopposing drive systems and the diameter of the outer track of each ofthe two opposing drive systems are substantially equal.

In some embodiments, for each flipper of the two opposing flippers, theplurality of outer pulleys comprise a front outer pulley and a rearouter pulley, and wherein the front outer pulley is pivotal about afront central hinge of the front wheel.

In some embodiments, a rotation of the inner track, the front wheel, therear wheel of the two opposing drive systems and a rotation of the outertrack of the two opposing flippers are synchronized.

In some embodiments, for each opposing drive system, the plurality ofinner pulleys comprises a front inner pulley and a rear inner pulley.

In some embodiments, each drive system of the two opposing drive systemsfurther comprises: a front central hinge configured to rotate the frontinner pulley and the front wheel in a common manner; and a rear centralhinge configured to rotate the rear inner pulley and the rear wheel in acommon manner.

In some embodiments, at least one flipper of the two opposing flippersis tilted on a plane parallel to the vertical plane.

In some embodiments, the at least one flipper has an operational modeand a folded mode.

In some embodiments, each flipper of the two opposing flippers may betilted independently with respect to the other flipper.

In some embodiments, the inner pulleys and the outer pulleys compriseannular projections; and the inner track and the outer track comprisemultiple cogs connected in a parallel manner forming a niche forreceiving the annular projections of the respective supporting pulleys.

In some embodiments, said ground robot is configured to be remotelycontrolled.

In some embodiments, the inner track extends along 70-130% of thecorresponding lateral side.

In some embodiments, the flipper extends along 70-130% of thecorresponding lateral side.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thefigures and by study of the following detailed description.

BRIEF DESCRIPTION OF THE FIGURES

Exemplary embodiments are illustrated in referenced figures. Dimensionsof components and features shown in the figures are generally chosen forconvenience and clarity of presentation and are not necessarily shown toscale. The figures are listed below.

FIG. 1 shows an isometric view of an exemplary ground robot;

FIG. 2 shows a side view of the ground robot of FIG. 1; and

FIG. 3 shows a front view of the ground robot of FIG. 1.

DETAILED DESCRIPTION

A drive system for a ground robot is disclosed herein. The drive systemmay allow an efficient use of tracks and flippers, which may be desiredwhen the ground robot traverses an unleveled and/or tough terrain,including, for example, obstacles or stairs. Furthermore, the disclosedtechnique avoids unnecessary use of a changing mechanism between awheeled drive (i.e., using wheels) and a tracked drive (i.e., usingtracks).

The term “about”, as used herein with respect to one or more values,including a range of values, may refer to the one or more values ±10%.

The term “track”, as used herein, may refer to a closed-loop structure,optionally polymeric and optionally flexible, used for groundpropulsion.

The term “robotic”, and its derivations as used herein, may refer to acontrollable computerized mechanical element or device.

The term “diameter”, as used herein with respect to a wheel or a pulley,may refer to an external and maximal diameter of the wheel or thepulley, i.e., including any projections they might have on theirexternal surface.

The term “diameter”, as used herein with respect to a track, may referto the diameter of the pulley, with the addition of twice the thicknessof the track mounted on it including the track projections.

Reference is now made to FIGS. 1, 2 and 3. FIG. 1 shows an isometricview of an exemplary ground robot (hereinafter “robot”) 100. FIG. 2shows a side view of ground robot 100 of FIG. 1. FIG. 3 shows a frontview of ground robot 100 of FIG. 3.

Ground robot 100 may include a main body 110 and two opposing drivesystems. Main body 110 may have a vertical plane (not shown) being,essentially, the sagittal plane of the main body. The vertical plane mayextend along a length of the main body and divide the body into twohalves, wherein each half includes one of the drive systems. Each one ofthe drive systems may include:

-   -   an inner track 140 disposed, for example, proximal to main body        110 and substantially parallel to the vertical plane, wherein        the inner track may be supported by a plurality of inner pulleys        such as a front inner pulley 150A and a rear inner pulley 150B;    -   a flipper 130 disposed, for example, distal to main body 110 and        substantially parallel to the vertical plane, wherein the        flipper may include a flipper body 170, an outer track 180 and a        plurality of outer pulleys such as a front outer pulley 190A and        a rear outer pulley 190B;    -   a front wheel 160A and a rear wheel 160B, both disposed, for        example, substantially parallel to the vertical plane and        between inner track 140 and flipper 130. Main body 110 and        correspondingly ground robot 100 may have a top 10, a bottom 20,        two opposing lateral sides 30, a front 40 (shown in FIGS. 2        and 3) and a rear 50 (shown in FIGS. 2 and 3).

Flippers 130 may be, for example, robotic elements which include amoving mechanism that may enhance the obstacle climbing capabilities ofthe ground robot.

Inner track 140 may extend along and may be supported by inner pulleys150A-B. Inner track 140 of each drive system may extend along thecorresponding lateral side 30, as shown in FIGS. 1 and 2. For example,inner track 140 may extend along 70-130% of the corresponding lateralside 30. Thus, inner track 140 may, for example, extend approximately tothe length of the corresponding lateral side 30 of robot 100. Frontinner pulley 150A and rear inner pulley 150B may be located at each oflateral sides 30. Each of front inner pulleys 150A may be locatedrelatively close to the front of ground robot 100 and rear inner pulleys150B may be located relatively close to rear 50 of ground robot 100, asshown in FIG. 1. Inner pulleys 150A-B may be mounted on main body 110.

Outer track 180 may extend along and may be supported by front outerpulley 190A and rear outer pulley 190B. Each flipper 130 and accordinglyeach outer track 180 may extend along the corresponding lateral side 30,as shown in FIGS. 1 and 2. For example, flipper 130 and outer track 180may extend along 70-130% of the corresponding lateral side 30. Thus,outer track 180 may, for example, extend approximately to the length ofthe corresponding lateral side 30 of robot 100. Front outer pulley 190Aand rear outer pulley 190B may be located at each of opposing lateralsides 30. Each of front outer pulleys 190A may be located close to thefront of ground robot 100 and each of rear outer pulleys 190B may belocated close to rear 50 of ground robot 100, as shown in FIGS. 1 and 2.Outer pulleys 190A-B may be mounted on flipper body 170.

Flipper body 170 and therefore flipper 130 may be mounted on front wheel160A. Front outer pulley 190A may be pivotal about a front central hingeof front wheel 160A to allow flipper body 170 and therefore flipper 130to be tilted with respect to main body 110, as shown in FIG. 2. Flipper130 may be tilted on a plane parallel to the vertical plain of main body110. Tiltable flipper 130 may be used for overcoming obstacles, such asstairs, and as further described below.

Flipper 130 may be mounted on front wheel 160A through a hinge, a joint,a pivot and/or another moveable link which enables flipper 130 to havean operational mode and a folded mode. In the folded mode flipper 130may be substantially parallel to and may extend along inner track 140and the corresponding lateral side 30 of main body 110. In theoperational mode flipper 130 may be tilted away from inner track 140 andthe corresponding lateral side 30 such that flipper 130 may no longerextend along them, as shown in FIGS. 1, 2 and 3. Each flipper 130 of thetwo flippers 130 may be tilted independently with respect to the otherflipper. For example, a right flipper 130 may be tilted in anindependent manner with respect to a left flipper 130 and vice versa. Insome embodiments, flippers 130 may be each rotated about a rotation axissuch as a hinge, a joint or a pivot in 360 degrees. Flipper 130 mayinclude a flipper motor for tilting flipper 130. The motor may be a DCservo motor. The flipper motor may rotate flipper 130 independently andregardless of the rotation of wheels 160A-B and outer pulleys 190A-B.

Front wheel 160A and rear wheel 160B may include a plurality of wheelprojections 165, on an external surface thereof, protruding outwardswith respect to front wheel 160A and rear wheel 160B accordingly toallow a hold of the terrain. Wheel projections 165 may be oblong and maybe positioned in a serial manner along the circumference of front wheel160A and rear wheel 160B accordingly. Front wheel 160A and rear wheel160B may be located at each lateral side 30 of ground robot 100. Frontwheel 160A may be located close to front 40 of ground robot 100 and rearwheel 160B may be located close to rear 50 of ground robot 100, as shownin FIG. 2. Front wheel 160A and rear wheel 160B may be positionedproximal to front inner pulley 150A and rear inner pulley 150Bcorrespondingly, proximal to inner track 140 and distal to main body110, as shown in FIGS. 1 and 3. Furthermore, front wheel 160A and rearwheel 160B may be positioned between inner track 140 and outer track180, as shown in FIG. 3. Front inner pulleys 150A and front wheel 160Amay be rotated about a front common axis, e.g., the front central hingeof front wheel 160A. Rear inner pulley 150B and rear wheel 160B may berotated about a rear common axis, e.g., a rear central hinge of rearwheel 160B.

Inner track 140 and outer track 180 may each be continuous, namely—forma closed loop. Inner pulleys 150A-B and outer pulleys 190A-B may receivetorque from a motor (not shown) and may transfer it to inner track 140and outer track 180 correspondingly by physically grasping the trackthereby setting the track into motion. Inner pulleys 150A-B and outerpulleys 190A-B may include annular projections. Inner track 140 and/orouter track 180 may include multiple cogs which may be connected in aparallel manner, forming a niche 155 for receiving the annularprojections of the respective supporting pulleys, as shown in FIG. 2.Inner track 140 may include a plurality of inner track projections 145,on an external surface thereof, protruding outwards with respect toinner track 140 and main body 110, as shown in FIGS. 2 and 3. Outertrack 180 may include a plurality of outer track projections 185, on anexternal surface thereof, protruding outwards with respect to outertrack 180 and flipper body 170, as shown in FIGS. 2 and 3. Inner trackprojections 145 and outer track projections 185 may be utilized to holdthe terrain and allow the mobilization of ground robot 100 by thetracks. Therefore, the combination of inner pulleys 150A-B and innertrack 140 and furthermore, the combination of outer pulleys 190A-B andouter track 180 may mobilize main ground robot 100.

According to an aspect of some embodiments, a reliability of the trackmay increase as measured by the chances of it being thrown off a pulley,get stuck or otherwise become unable to mobilize a platform. Thestructure of the annular projections of the pulleys which may fit intothe niches between the cogs may centralize the tracks in a way thatincrease tracks' reliability.

A rotation of inner tracks 140, front wheels 160A and rear wheels 160Bof the opposing drive systems and a rotation of outer tracks 180 ofopposing flippers 130 may be synchronized. For example, each of theopposing drive systems may be propelled by a drive motor. The drivemotor may be, for example, a brushless DC motor that drives a spur geartype gearbox. The two drive motors may be connected at the front part ofmain body 110. For each opposing drive system, the drive motor maytransfer torque to front pulley 150A. Front pulley 150A may spin innertrack 140, which then may spin rear pulley 150B. Rear pulley 150B may berigidly and operatively coupled with rear wheel 160B. Front pulley 150Amay be rigidly and operatively coupled with front wheel 160A. Frontwheel 160A may be rigidly and operatively coupled with front outerpulley 190A. These rigid couplings may transfer the torque to front andrear wheels 160A-B and to outer track 180 of each flipper 130. Frontouter pulley 190A may spin outer track 180 which then spins rear outerpulley 190B. Thus, front inner pulley 150A, front wheel 160A and frontouter pulley 190A may be the “drivers” while all the other pulleys andwheels may be idlers.

A diameter of front wheel 160A and rear wheel 160B of each of theopposing drive systems may range between 1.2 to 1.3 times of a diameterof inner track 140. The diameter of front wheel 160A and rear wheel 160Bof each of the opposing drive systems may range between 1.2 to 1.3 timesof a diameter of outer track 180. A diameter of a track according to thedisclosed technique is illustrated in FIG. 2 with respect to outer track180, indicated “D”. In some embodiments, the diameter of inner track 140and outer tracks 180 may be substantially equal. For example, innertrack 140 and outer track 180 may have an equal diameter of 130millimeter. The diameter of front wheel 160A and rear wheel 160B may be160 millimeter. The ratio between front wheel 160A and rear wheel 160Bdiameter and inner track 140 and outer track 180 may be then 1.23.

The ratio may allow efficient use of the inner and/or outer tracks andmay allow avoiding the use of a changing mechanism between a wheeleddrive, which may be preferred in a leveled terrain, and a tracked drive,which may be preferred in an unleveled and/or rough terrain such asstairs. A configuration of the outer and/or inner pulleys and the frontand rear wheels, such as when all are pivotal about a single centralhinge of the front wheel and a single central hinge of the rear wheelcorrespondingly, may allow for the inner and/or outer tracks to float(i.e., not touch the ground) when the ground robot traverses a leveledterrain. Thus, in a leveled terrain, only the front wheels and rearwheels may be used and the inner and/or outer tracks may not interferewith the movement of the ground robot. Furthermore, such configurationmay decrease the level of noise, when the ground robot drives on aleveled terrain, as the contact area between the ground robot and theterrain may be smaller. Thus, the tactical capabilities of the groundrobot may be enhanced. On the other hand, when the ground robottraverses an unleveled and/or rough terrain, the ratio between thewheels and the inner and/or outer pulleys allows efficient use of thetracks, which now may assist and participate in the movement of theground robot by contacting the terrain.

The ratio between the diameter of the tracks and the wheels maydetermine the extent of the use of the tracks with respect to terrainlevel differences encountered by the ground robot. That is to say, asthe tracks diameter is larger and closer to the wheels diameter, asmaller terrain level difference may lead to involvement of the tracksin the ground robot drive. In such a case the extent of the tracksinvolvement in the ground robot drive may be larger. On the other hand,as the tracks diameter is smaller with respect to the wheels diameter,only a larger terrain level difference may lead to involvement of thetracks in the ground robot drive. In such a case the extent of thetracks involvement in the ground robot drive may be smaller.

In some embodiments, the ground robot may be remotely controlled, interalia, to climb obstacles including, but not limited to, stairs, ditches,rocks, sewer tunnels, and uneven rough terrain.

In some embodiments, the length of the flipper and/or the main body maybe about 67 cm or more, which is the minimal length required forclimbing a standard stair case by a ground robot, which has three pointsof contact with the stairs.

In some embodiments, the main body may be shaped with opposite central(upper and lower) niches, for example forming a shape similar to thesign infinity “∞”. The lateral sides' shape may be curved and/or similarto the “infinity” sign, having round edges and a narrowing middle part.Optionally, lateral protection covers are also shaped with opposingniches to enable stretching the inner track and to prevent a collisionbetween the inner track and the main body and/or the lateral covers.This shape may enable the ground robot to climb stairs and/or othervertical obstacles, as it prevents collisions between the narrow part ofthe infinity shape and the vertical obstacle and it may maximize thecontact with the terrain on both sides of the vertical obstacle. Theshape may also reduce the weight of the main body compared to a similarmain body without an infinity shape.

In some embodiments, the flipper body may be shaped in an infinity shapeencircled with the outer track, such as flipper body 170 as shown inFIGS. 1 and 2. The flipper body may have a bottom, top and lateral sidescorresponding to the bottom, top and lateral sides of the ground robot.Optionally, a flexible outer track may be mounted on the infinity shapedflipper. The outer track may flex towards the narrow part of theinfinity shape upon climbing over an obstacle, and/or application ofexternal pressure. Optionally, the flipper body may preserve a distancebetween the outer track and the bottom of the flipper body. This is inorder to avoid friction between the outer track and the flipper bodywhile the outer track is flexed upwards, e.g., by traversed obstacles orstairs. Optionally, the bottom side and the top side of the infinityshaped flipper body are symmetric. Optionally, the bottom side and thetop side symmetry enable the ground robot to flip bottom to top andfunction in a similar manner in both configurations.

In some embodiment, the right and/or left flippers may also be mountedin different locations with respect to the ground robot. In someembodiments, the flippers may be low weight flippers therebycontributing to overall ground robot low weight, which may beadvantageous for higher speed and maneuverability.

In some embodiments, the ground robot may optionally have one or moreimage sensors 195, mounted in or on the main body, directly or by amoving or a static carrier. Image sensor 195 may be a 3D vision camera.Image sensor 195 may provide images of the ground robot's surrounding toan operator of the ground robot. Furthermore, image sensor 195 may beutilized to perform autonomous operations by the ground robot, such asmovement.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible sub-ranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A vehicle comprising: a main body; at least oneflipper disposed on the main body; and two drive systems disposedlaterally to the main body, wherein each drive system comprises: a tracksupported by pulleys, a front wheel disposed near a front end of thetrack, and a rear wheel disposed near a rear end of the track; wherein adiameter of the front wheel and the rear wheel is larger than a heightof the track, wherein the height of the track is the addition of thediameter of the pulleys and twice the thickness of the track mounted onit.
 2. The vehicle of claim 1, wherein a diameter of the front wheel andthe rear wheel ranges between 1.2 to 1.3 times of the overall eight ofthe track, thereby allowing both the track and wheels to engage theground simultaneously.
 3. The vehicle of claim 1, wherein said at leastone flipper comprises at least one wheel.
 4. The vehicle of claim 1,wherein each of said at least one flipper comprises a flipper tracksupported by flipper pulleys.
 5. The vehicle of claim 1, wherein atleast one of the track, the wheels, and the flipper comprise, on anexternal surface thereof, at least one of a tread pattern and aplurality of projections, both for increasing a ground traction.
 6. Thevehicle of claim 3, wherein any of the diameter of the pulleys and thediameter of the flipper pulleys of the two drive systems aresubstantially equal.
 7. The vehicle of claim 3, wherein the at least oneflipper is adapted to rotate around an axis parallel to the axis of atleast one of the pulleys and the wheels.
 8. The vehicle of claim 1,comprising two flippers disposed laterally to the main body, wherein oneof the two flippers rotates independently with respect to the other ofthe two flippers.
 9. The vehicle of claim 3, wherein the flipper isrotationally positioned parallel to the main body during normaloperation and is rotated to project from the main body to overcomeobstacles.
 10. The vehicle of claim 1, wherein the track and the wheelsare adapted to rotate independently.
 11. The vehicle of claim 1, whereinthe track and the wheels are adapted to rotate in synchronicity duringnormal operation and are adapted to rotate independently when normaloperation results in loss of traction of the vehicle.
 12. The vehicle ofclaim 1, wherein the vehicle is a ground robot.
 13. A drive system for avehicle comprising: a track supported by pulleys; a front wheel disposednear a front end of the track; and a rear wheel disposed near a frontend of the track; wherein a diameter of the front wheel and the rearwheel is larger than a diameter of the track.
 14. The drive system ofclaim 12, wherein a diameter of the front wheel and the rear wheelranges between 1.2 to 1.3 times of the overall height of the track,thereby allowing both the track and wheels to engage the groundsimultaneously.
 15. The drive system of claim 12, wherein at least oneof the track and the front wheel, and the rear wheel comprise, on anexternal surface thereof, at least one of a tread pattern and aplurality of projections, both for increasing a ground traction.
 16. Thedrive system of claim 12, wherein the track and the wheels are adaptedto rotate independently.
 17. The drive system of claim 12, wherein thetrack and the wheels are adapted to rotate in synchronicity duringnormal operation and are adapted to rotate independently when normaloperation results in loss of traction of the vehicle.
 18. The drivesystem of claim 12, further comprising at least one flipper, wherein theat least one flipper comprises at least one of a flipper track supportedby flipper pulleys and a wheel.
 19. The drive system of claim 18,wherein the at least one flipper is adapted to rotate around an axisparallel to the axis of at least one of the pulleys and the wheels
 20. Amethod for operating a ground robot, comprising: instructing a groundrobot, wherein the ground robot comprises tracks supported by pulleysand comprises wheels, to perform track motion using the track when thewheels do not provide enough ground traction; instructing a ground robotto perform wheel motion using: at least one front wheel that is disposednear a front end of each track, and at least one front rear wheel thatis disposed near a rear end of each track, wherein a diameter of said atleast one front and rear wheels is larger than the height of the tracks,and wherein the height of the tracks is the addition of the diameter ofthe pulleys and twice the thickness of the track mounted on it; andinstructing a ground robot to perform flipper motion using at least oneof said wheels and said track, with at least one rotatable flipper,wherein said at least one flipper is rotated to align with a main bodyof said ground robot during said track motion and said wheel motion,wherein said at least one flipper is rotated to extend from said mainbody during said flipper motion, and wherein said at least one flippercomprises at least one of a flipper track supported by flipper pulleysand a flipper wheel.